The present invention is directed to a mounting structure for a reflector which is deployed from a stowed position during launch to an extended position when the satellite obtains orbit. The deployed reflector is aligned with its associated feed horn and sub-reflector in the deployed position.
Space satellites require antennas for signal reception and/or transmission. Such satellites and antennas must be relatively lightweight, strong, capable of being stowed into compact condition, and capable of being activated remotely into deployed condition in which they are operational for their intended purposes. The antenna systems generally consist of a reflector, feed horn, and a sub-reflector. It is generally desirable to use antenna reflectors which are attached to the supporting spacecraft platform by hinges so that they can be pivoted up against the sides of the spacecraft in a streamlined stowed position during the launching of the spacecraft. Once the satellite is launched into orbit, the reflector may be deployed by pivoting the reflector away from the body of the satellite into its operational position.
As shown in FIG. 1, a single axis mounting structure is used to connect the reflector to the spacecraft body. The mounting structure consists of a hinge secured to the bottom of the spacecraft which allows actuators associated with the hinge to swing the reflector outward for operational deployment. A mounting structure of this type is described in commonly owned U.S. Pat. No. 5,673,459. Deployment in the system of the ""459 patent is actuated by a bias spring which pivots the reflector outward upon release of holddowns.
Reflectors must be maintained in alignment with its signal source or target after deployment. This is particularly critical in communication applications where the reflector needs to be accurately aligned with its associated signal feed horn. Therefore in some applications it is necessary to adjust the position of the reflector further to obtain full operational deployment. Deployment in such applications, may involve rotating the antenna supports on a hinge axis to unfold the reflectors to a position in which they extend perpendicular to the sides of the spacecraft, and also rotating the reflectors about a second axis, perpendicular to the first axis, to aim the reflectors in the direction of the signal source or target. Actuators which provide such two axis movement have been devised as illustrated in U.S. Pat. No. 5,864,320.
It has been found that the alignment between reflector and feed can be significantly distorted by differential thermal stress between the two elements. This distortion is compounded in the configurations of the prior art by mounting the reflector at the bottom of the spacecraft body and mounting the feed horn at the top. This distance is mandated by the aligned physical relation between reflector and feed and the limited amount of movement available for deployment. Generally the feed remains fixed and the reflector moves into the deployed position.
It is a purpose of this invention to minimize the thermal differential between the reflector and feed and thereby maintain the aligned relation in the deployed position. Another purpose of this invention is to mount the reflector support structure in close proximity to the feed apparatus. It is a purpose of this invention to accomplish the deployment using multiple two axis actuators. In addition it is a purpose of this invention to provide a antenna sub-module incorporating these features which will facilitate the testing and installation of the antenna system.
A satellite antenna sub-module is constructed in which the signal feed and sub reflector are secured in a fixed mutual relation on a frame which is to be, in turn, assembled within a spacecraft/satellite. The associated primary reflector is mounted on the frame by means of a support boom at a location on or in close proximity to the feed attachment point. The attachment points of the primary reflector boom and the associated feed horn and sub-reflector are positioned as close as possible in order to minimize thermal distortion throughout the reflector system. The boom is connected at one end to the frame by means of a two axis actuator which provides powered rotary motion about two orthogonal axis"". The reflector is mounted at the other end of the boom by a second similar two axis actuator.
By sequentially rotating the boom and reflector through a series of movements, the reflector is deployed from its stowed position, where it is secured for launch, to its fully deployed position, in which it extends outward from the side of the space craft for operation in alignment with its feed horn and sub-reflector.
The reflector system described above is constructed for use in satellites having multiple antenna which must be stowed in a nested relation to present a streamlined contour for the exterior of the spacecraft while the craft is being launched into orbit. To properly nest the multiple antenna they are mounted in pairs on independent booms as described above.